How to Save Seeds from Biennial Plants

Take your seed-saving know-how to the next level by learning how to keep seeds from open-pollinated biennials, including beets and Swiss chard.

By Lee Buttala

| Summer 2017

Beets and Swiss chard are forms of the same species, Beta vulgaris. If different varieties of these plants are in flower at the same time, they can easily cross-pollinate and produce seeds that will not be true to type.Photo by iStock/sorendls

To save seeds from Swiss chard, dig it up, trim the leaves to about 3 inches in length, and then replant in containers with slightly moist potting mix or sand before placing them in cold storage. Photo by iStock/brandtbolding

Younger plants, provided they’re of reproductive size (typically having eight or more true leaves), are less susceptible to winter cold and are often set out late in the season to overwinter.Photo by iStock/FatCamera

Mature beet plants may reach four to five feet in height and take up a significant amount of space.Photo courtesy Seed Savers Exchange

Beets can be replanted in spring to flower and go to seed. Photo courtesy Seed Savers Exchange

Beets can be dug up, stored with their tops cut short, and then replanted in spring to flower and go to seed. Photo courtesy Seed Savers Exchange

Rainbow chard is coveted for its brightly colored stalks. Each color is in fact its own cultivar and must be isolated from the others when flowering to pass its color on to the next generation. Photo by iStock/dancingfishes

The small, relatively inconspicuous flowers of Swiss chard and beets are typically pollinated by wind, which is why they require an isolation distance of 800 feet or more from other flowering varieties of B. vulgaris. Given the biennial nature of this species, this isn’t hard to manage.Photo courtesy Seed Savers Exchange

One of the most common mistakes for novice seed savers is to not allow the seed to mature thoroughly before harvesting. Although seeds may continue to dry and harden, seeds don't really continue to mature after the seed heads have been cut from the plants. B. vulgaris seeds should have turned from green to tannish-brown before being collected. The spikes mature sequentially from the base of the flower stalks upward.Photo courtesy Seed Savers Exchange

Those who grow broccoli and cauliflower without saving the seeds will still benefit from understanding vernalization. For these plants to produce their flower heads (which are what we eat in immature form), they need to be exposed to a certain amount of cool weather to induce flowering. Most of these crops typically need 1 to 4 weeks of cumulative temperatures below 50 degrees after they’ve reached sexual maturity. Photo by Adobe Stock/mushy

We save seedsfor many reasons: tradition; the idea of seed sovereignty and not being beholden to seed companies; and ensuring that our favorite cultivars don’t disappear. The most obvious reason for seed saving is that we want more plants. And when it comes to saving our favorite vegetable seeds, more plants mean more food. But some vegetables are easier to bring to seed than others. Self-pollinating annuals, such as lettuce and beans, are the easiest from which to save seed. These are followed by other annual crops, such as tomatoes, pumpkins, or peppers, which may require some level of isolation or pollination management, but other than that are grown similarly to how they’re grown for eating.

Biennial crops (varieties that flower, bear fruit, and set seed in their second season before reaching the end of their life-cycle, such as beets, chard, and many brassicas) are more challenging to grow for seed and require a deeper understanding of botany and the processes that bring plants to seed in the first place. Additionally, biennials grown for seed are brought to a state that we aren’t as familiar with, because we typically harvest these plants in their first year.

Basic Seed Saving

Some principles of seed saving are universal, no matter which crops are being grown for seed. Seeds are the product of the fertilization of a plant’s flowers, which brings about fruit and seed production. Seeds that are true to type (seeds that bear the traits of their parent) can only be saved from open-pollinated cultivars that are isolated from cross-pollination with other varieties within their species. This can be confusing because some species contain more than one crop type, and the flowers of these plants can cross with one another if they’re in bloom at the same time. Cabbages, collards, cauliflower, European kales, kohlrabi, broccoli, and Brussels sprouts are all members of the same species, Brassica oleracea. Beets and Swiss chard are also forms of the same species, Beta vulgaris. If different varieties of these plants are in flower at the same time, they can easily cross-pollinate and produce seeds that will not be true to type, or characteristic of their variety. Additionally, some of these crops are self-incompatible, meaning that the pollen from a separate, genetically distinct plant of the same variety must fertilize its flowers to produce true-to-type seeds. In this case, more than one plant has to be grown, although growing a larger population of plants is always a good thing because it helps to maintain genetic diversity.

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The cole crops of B. oleracea have an added complication in that some of the crop types within the genus are annual and flower in their first season, while others are biennial and flower after overwintering. If growing these for seed, you’ll need to make sure only one variety within the species is in flower at a time to prevent cross-fertilization. Whatever the crop, in order to flower and bear seed, biennial plants must reach a certain size (reproductive growth is typically possible after plants have eight or more true leaves) and then be exposed to a certain amount of cold for a period of time to trigger flowering and subsequent fertilization. This cold treatment is known as “vernalization” and is critical in bringing biennial crops to seed. The difficulty of this process is that the proper vernalization temperatures need to occur for a cumulative (non-consecutive) length of time without temperatures getting so cold that they damage the crop. In some areas, this is done by creating the necessary conditions in a managed way — by digging plants, potting them up, and storing them in a cold cellar or garage; or by digging roots of some crops, such as carrots and beets, and storing them in a refrigerator so they’re exposed to the cold they need without being damaged by temperatures that dip low enough to damage the plants. In some regions of the country, these conditions occur naturally while the plants are still in the ground, making the whole process much easier to manage.

It’s important to remember that these plants need to reach a minimum size and maturity before vernalization so they’re able to set seed in the second season, and this usually involves having eight or more leaves in the first season or a stem that’s about 1/2-inch in diameter. Surprisingly, younger plants are often better adapted to surviving winter than larger plants, so seed savers will often direct sow or set them out in summer to attain the ideal size before the plants are ready to be overwintered.

A simple rule of thumb is to remember that biennial crops require three things to produce seeds in the second season: to be sexually mature enough before vernalization to be triggered to flower; to be exposed to proper vernalization temperatures (typically 8 to 10 weeks of cumulative temperatures below 50 degrees Fahrenheit for most brassicas, and 10 weeks below 40 degrees for B. vulgaris, but this can vary from biennial to biennial and even within a species); and to survive the winter as disease-free as possible.

Growing Beets and Swiss Chard for Seed

In the case of beets and Swiss chard (B. vulgaris), these crops will typically survive in areas with minimum temperatures in the upper teens, and this can often be mitigated further through the addition of a straw mulch, leaves, or a floating row cover. If you’re in an area that’s either too cold or not cold enough to properly vernalize these crops, then you must dig them up and store them somewhere cool to induce vernalization. Dig up and trim beets to just above the crown, and store them in a ventilated container lined with wood shavings or sand. Remove any disease-ridden roots before storage. Dig up Swiss chard, trim the leaves to about 3 inches in length, and then replant in containers with slightly moist potting mix or sand before placing them in cold storage. It’s important not to damage the growing point of the plant when trimming it back. The ideal temperature for storage is about 35 degrees with humidity levels above 75 percent if possible. Garages, root cellars, and unheated sheds can work well for this.

As the ground becomes workable in spring, set the plants back into the ground about 2 feet from the center of each plant so they can reach their full size at seed maturity. Both beets and chard will put on new growth before flowering and setting seed. The flower spikes will reach about 4 feet tall, so you’ll need to stake them as the seeds mature. Seeds usually develop by midsummer in the northern half of the United States. Because this species bears self-incompatible flowers, you should grow at least five plants to ensure proper seed set. And, you’ll want to grow these plants at a distance of 800 feet or more from other flowering plants of the same species, which you can easily manage by bringing just one variety at a time to flowering size. After seeds have matured and leaves become tannish-brown, cut down the seed stalks; set them in a cool, protected place to dry for 7 to 14 days; and then thresh and clean them.

For home seed savers, the simplest threshing method is to run a gloved hand down the length of the stalk, with a container placed underneath to catch the dislodged seeds and chaff. Discard the stalks, and then screen and winnow the seeds to remove the chaff. Chaff (the remainder of the stalks and leaves) can harbor disease and is best removed as thoroughly as is reasonably possible. Store seeds in a cool, dry place, where they should remain viable for up to five years. (I prefer storing them in paper envelopes.)

The most important detail — and one that’s often forgotten — is to label seeds with the cultivar name and the date they were harvested. All cultivars of chard and beets look the same when you grab them the following season, and there’s nothing more frustrating than having done all the work only to find yourself struggling to remember which cultivar you’ve saved.

Biennial Crops and Their Families

A variety of crops are biennial in nature and require two growing seasons in order to produce seeds. A somewhat complete list by family includes:

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